Embodiments of the invention relate to a dual-fuel internal combustion engine with the features of the preamble of claim 1 and a method for operating a dual-fuel internal combustion engine with the features of the preamble of claim 7.
Dual-fuel internal combustion engines are typically operated in two operating modes. We differentiate an operating mode with a primary liquid fuel supply (“liquid operation” for short; in the case of the use of diesel as a liquid fuel, it is called “diesel operation”) and an operating mode with primarily gaseous fuel supply, in which the liquid fuel serves as a pilot fuel for initiating combustion (also called “pilot operation”, “dual-fuel operation” or “ignition-jet operation”).
In pilot operation mode, in which the liquid fuel is introduced as a pilot fuel, the regulating device is designed to control the fuel injector and the at least one gas supply device for selective metering of the quantity of liquid or gaseous fuel supplied to the at least one piston-cylinder unit.
In diesel operation, it is known that the combustion process can be moderated by varying the pilot injections, main injections and after-injections. Such operating modes with multiple injections are known e.g. from DE 602 16 437 T2, EP 2 806 140 A1, US 2012/0325180 or WO 2003/027473 A1.
U.S. Pat. Nos. 7,305,972, 7,769,530, DE 10 2014 000 326 A1, DE 10 2014 004 976 A1 and EP 1 730 394 disclose injectors and control concepts suitable for this purpose.
With regard to the load requirement placed on an internal combustion engine, a distinction can be made between steady-state operation and transient phases.
If the load requirement moves within a relatively narrow band (e.g. if changes in the load requirement are below about 10% of the current load), this is called steady-state operation.
If there are larger changes in the load requirement, the transition from the former to the new load requirement is called a transient phase.
In diesel operation of the internal combustion engine, it is possible to map rapid changes in the load requirement and the internal combustion engine thus has favorable behavior in the transient phase (in short: transient behavior).
In diesel operation, the power is adjusted by adjusting the fuel quantity (fuel-guided system).
If, however, the internal combustion engine is primarily supplied with gaseous fuel, rapid adaptation of the power output of the internal combustion engine to changed load requirements is not possible. Simply supplying more gaseous fuel is ruled out, since the internal combustion engine then starts knocking. An internal combustion engine in pilot operation therefore has an unfavorable transient behavior.